British police on Saturday arrested an 18-year-old man in connection with attack on a London Underground train in Parsons Green. Meanwhile, the threat level in the country continues to be 'critical'.

The Independent reported that the man was arrested in the departure area of the port of Dover under the Terrorism Act on Saturday morning by Kent Police.

The Metropolitan Police described the arrest as "significant" but did not give any further information on the man's alleged role, having previously suggested investigators were hunting multiple suspects.

The Independent quoted Deputy Assistant Commissioner Neil Basu, the senior national co-ordinator for counter-terrorism policing, as saying that "this arrest will lead to more activity from our officers. For strong investigative reasons we will not give any more details on the man we arrested at this stage".

Basu also said that the investigation continued and the threat level remained at critical. Detectives have so far spoken to 45 witnesses are receiving photos and videos from the public, while scouring CCTV footage.

British Prime Minister Theresa May on Friday raised the threat level from severe to critical after an explosion on a Tube train in south-west London in the morning.

This is the fourth time that the assessment has been placed at the highest level in the past 11 years. Critical means an attack is expected imminently.

The UK's threat level was upgraded from "severe" to "critical" on May 23 following the Manchester bombing on May 22, in which a bomb exploded in the foyer of Manchester Arena moments after US pop star Ariana Grande left the stage. The attack left 22 dead and 59 injured.

Islamic State (IS) claimed responsibility for the explosion on Friday in which 29 people were hurt after an Improvised Explosive Device (IED) blasted on a Tube train at the Parsons Green Station.

The explosion during Friday's morning rush hour also left several passengers fleeing in panic.

Passengers suffered facial burns after the incident inside the carriage as it was sat at the overground station.

Police said a device was placed inside a bag and left by the tube carriage door before exploding towards the rear of the train, filling the carriage with smoke.

Passengers were seen "running and screaming" from the tracks.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)